1. Field of the Invention
The present invention relates to wafer processing, and more particularly to apparatus and methods for creating Double Pattern (DP) structures on a patterned wafer in real-time using Dual Pattern Contact-etch (DPCE) processing sequences and associated Contact-Etch-Multi-Input/Multi-Output (CE-MIMO) models.
2. Description of the Related Art
Etch process behavior is inherently non-linear and interacting step-to-step (layers), or as process stacks are compiled (etch/cvd/implant). With the knowledge of the process interactions based on physical modeling of Tokyo Electron Limited (TEL) chambers and base processes and imperial data and measurements from process refinement and tuning the control of Critical Dimension (CD), Sidewall Angle (SWA), depths, film thicknesses, over etching, undercuts, surface cleaning and damage control can be recursively calculated and optimized using multi-input multi-output non-linear models. Current low cost products use a bulk silicon technology. As the transistor continues to shrink, the impact of the channel depth is becoming critical (ultra-shallow source/drain extensions). As the Silicon-on-Insulator (SOI) film shrinks, smaller variations in the gate and/or spacer thickness and thickness of the SOI film can affect the transistor's performance. When etch procedures are not controlled, the removal of the material near the gate affects the electrical performance.
Current high performance microprocessors use PD SOI (partially depleted Silicon-on-Insulator film—giving a threshold voltage 0.2 volts. PD SOI films are around 50 nm thick while the gate and/or spacer reduction amount can be a large percentage (10%) of the total gate and/or spacer thickness. Future generations of SOI films are called FD SOI (fully depleted SOI), giving a threshold voltage 0.08 volts and a thickness of ˜25 nm). Currently these films are not in production due to limitations in thickness control uniformity and defects. Channel mobility degrades with decreasing SOI thickness. With thinner films, the control of the metal-gate structures becomes more critical